Allan Massie lives deep in the Scottish borders where distractions are few, especially if, like him, you do not drive.

Following the cryptic directions he sent me, after three wrong roads, a couple of three-point turns and a shame-faced phone call for guidance, I eventually find him. Though only a few miles out of Selkirk, his elegant country house feels utterly secluded. Hidden by trees, it faces fields of cattle across a milky green pond where a rowing boat lies on the bank, ready for a dip.

If ever a house cried out to be put into a novel, this is it. "It's rather shabby, I'm afraid," says Massie, obviously fond of the place he shares with his wife, two Clumber spaniels and four cats, as well as chickens and horses. But as he leads me along a book-lined passage to a parlour with a sizzling coal fire - once the servants' quarters, with a bell panel showing six bedrooms, dining room, tradesman's entrance and the like - it is clear that the novelist's imagination is working on material much further from home.

Now in his mid-seventies - Massie was born in 1938 in Singapore in Malaya, where his Aberdeenshire father was a rubber planter - he is almost as prolific and certainly every bit as enquiring as when he started out. Unlike any other novelist in the country, he has combined a high-profile career as a novelist with the daily demands of freelance journalism, writing prolifically on politics, sport and books for such publications as the Daily Mail, Daily Telegraph, The Scotsman, Sunday Times and the Spectator. If nothing else, being one of the few Tory writers in Scotland, he tells me through a perpetual cloud of cigar smoke, has been useful in terms of paying the bills.

Beyond his impressive weekly word count for the press, Massie has more than 20 novels behind him, notably his acclaimed loose trilogy set in mid-20th-century Europe, A Question Of Loyalties, The Sins Of The Fathers and Shadows Of Empire, and his bestselling Roman novels, which began with Augustus.

Recently, however, he has embarked on a new direction with a series of crime novels set in Vichy France, the era he evoked so memorably in A Question Of Loyalties.

Featuring the quiet and contemplative war veteran Superintendent Lannes, this projected trilogy, which began with Death In Bordeaux and Dark Summer In Bordeaux, is followed later this month by Cold Winter In Bordeaux. But now, instead of being a trilogy, a fourth title is in the pipeline "by popular demand", says his publisher.

While much crime fiction comes in series, Massie's books are stretching the definition of the genre, as he is well aware. "I originally intended I would write a crime novel. But having decided to set them during the war then obviously they are not. They are unorthodox crime novels because, with the first two, they know who the killer is, but there's no arrest, there's no trial."

He sounds unapologetic, and why not. Part of the attraction of these immensely readable tales is not the solving of the crime but what the investigation reveals about Lannes and his times. Death In Bordeaux was a lean, moody tale, whose atmosphere clings to the page like cologne. One could not read it without catching an echo of Georges Simenon. Asked if he was an influence, Massie laughs. "Oh yes. Simenon is one of my favourite writers. It's exactly the sense of ambience and the clarity, the lack of anything superfluous in his novels, that is what I particularly admire. And the sense of place too, of course. Lannes started out in my mind as a sort of Maigret figure, but he has actually moved quite a bit away from Maigret."

A family man, father of two grown sons and a daughter, as is Massie, Lannes has one law-abiding son working for the Vichy government, and the other intent on joining General De Gaulle's Free French brigade. Added to which, the superintendent is under orders, like all the police, to collaborate with the Germans. Life could scarcely be more awkward for him, or the various denizens of occupied Bordeaux than in the years the books cover, from 1940 to 1944, where the fourth book will conclude, after the Liberation and the dreadful reprisals that followed.

"The period fascinates me," he muses, "because it was so difficult to do what was right. What do you do in a position like that?"

Surrounded by a Corryvreckan of idealists - Communists, Nazis, collaborators, Free French, the Resistance, and more - Lannes is a steady presence in their midst. Like other of Massie's characters, he looks on idealism as a curse.

This being a recurring theme, one wonders if it springs from a philosophical interest, or something more personal.

"It's a fascinating subject philosophically," Massie replies, in his smoky, gentle voice, ignoring the scratching and yelping of a spaniel at the door. "One subject where the opposition is most clearly expressed is in Shadows Of Empire. There's a scene in the postwar part of that, when the narrator visits his friend from schooldays, who is now a doctor in Edinburgh, in Gorgie. The doctor, who is the moral centre of the novel, really, he says, 'To hell with ideology, I believe in ethics'.

"Lannes is in that position too. He detests ideology, he believes in ethics, there are things which are right and which are wrong. But it's not as simple as that because sometimes you have to collaborate with what might be wrong.

"At the end of the first novel, Death In Bordeaux, he has gone to Vichy and got help from a minister there, and he has compromised himself, he knows that. And in this novel he also does something which a policeman should never do, but he thinks it's the right thing to do... From some points of view he behaves badly in all three novels. And yet I think he's a good man."

As with all his works, the Bordeaux books teem with believable characters, evoked as vividly as if they were people he's known all his life. There are prostitutes of both sexes, criminals who are petty and vicious, closet homosexuals, venal politicians, corrupt officials, and housewives eaten alive by worry.

Yet while some are clearly misguided, and others deeply unpleasant, their creator remains remarkably non-judgmental.

"I hope so," he says, "because once you become judgmental, you're feeling superior to your characters. In novels such as this you are placing your characters in positions that you have never been in yourself, and what you are really asking is, how would you behave in these conditions? And I don't think you have any right to say I would have behaved much better than they would.

"Okay, there are some people who are bad, but they are bad as seen by other characters, and others who are feeble, like Lannes's immediate superior, who's quite a strong man but a feeble man, because he's determined that he's going to survive and he's going to be in this position at the end of the war, no matter how things turn out. There's a line about how 'his backside is creased from sitting on the fence'."

Massie chuckles, and one catches a glimpse of the fascination with the predicaments of others, which is his hallmark. His writing style has been likened to that of Graham Greene, yet while the similarities in terms of moral complexity and personal angst are plain, his tone is less mournful, more spirited, despite the bleakness of his outlook.

As the Bordeaux series unfolds, so do the complexities of the Lannes family. Cold Winter In Bordeaux sees them deepen further still, as his sons follow their different paths. In this, again, Massie revisits a preoccupation seen most clearly in Sins Of The Fathers, about the son of a Nazi criminal and daughter of a Jewish collaborator. One cannot help wondering about his own father, and their relationship.

"I didn't know him really until I was grown up," Massie replies, "because he was a Japanese prisoner-of-war, and then he went back to Malaya in '46, '47. And then he and my mother got divorced, he married someone else." By the time his father had returned to England, Massie was at school at Glenalmond. "He came and took me out for lunch sometimes."

But what came next was unexpected. After retiring from farming in Hampshire, he decided he was going to leave his second wife. "He turned up on my mother's doorstep in Deeside and said this was going to happen and he'd like to come back."

Massie gives a bark of laughter. "She said she'd have to think about it. She consulted my brother, my sister and myself, and we all gave her the same answer: 'We can't decide for you. It's up to you.' And then he came back, and they married, and they had actually a generally happy last 15 or 16 years."

One can speculate, fancifully perhaps, that the father's experience of war influenced his son's absorption with the past. But even were this the case, Massie's reasons for writing about earlier eras rather than our own times, he says, are exceedingly simple.

"It's quite clear from the sort of novels I've wanted to write, which are almost all novels in which public life and private life, the way they intertwine, is the subject. They are almost all ones in which public life may involve not just disgrace but death. When I'm asked about this at book festivals I've often quoted the line of MacDiarmid's: 'the trouble with Scotland is that there's nobody worth killing'."

He smiles, and reaches for another Toscano cigar. "I suspect he made an exception for himself, and thought he would be worth assassinating. But there is something in it. If you are writing a political novel set in Scotland or even London today, politics is not a matter of life and death. That's the real reason."

Cold Winter In Bordeaux is published by Quartet, £12. Allan Massie will be speaking at two events at Aye Write! Book Festival, on Saturday April 5.